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    Subject[PATCH -mm] do_migrate_pages() calls migrate_to_node() even if task is already on a correct node
    While moving tasks between cpusets I noticed some strange behavior.  Specifically if the nodes of the destination
    cpuset are a subset of the nodes of the source cpuset do_migrate_pages() will move pages that are already on a node
    in the destination cpuset. The reason for this is do_migrate_pages() does not check whether each node in the source
    nodemask is in the destination nodemask before calling migrate_to_node(). If we simply do this check and skip them
    when the source is in the destination moving we wont move nodes that dont need to be moved.

    Adding a little debug printk to migrate_to_node():

    Without this change migrating tasks from a cpuset containing nodes 0-7 to a cpuset containing nodes 3-4, we migrate
    from ALL the nodes even if they are in the both the source and destination nodesets:

    Migrating 7 to 4
    Migrating 6 to 3
    Migrating 5 to 4
    Migrating 4 to 3
    Migrating 1 to 4
    Migrating 3 to 4
    Migrating 0 to 3
    Migrating 2 to 3


    With this change we only migrate from nodes that are not in the destination nodesets:

    Migrating 7 to 4
    Migrating 6 to 3
    Migrating 5 to 4
    Migrating 2 to 3
    Migrating 1 to 4
    Migrating 0 to 3

    Signed-off-by: Larry Woodman<lwoodman@redhat.com>

    diff --git a/mm/mempolicy.c b/mm/mempolicy.c
    index 47296fe..2bd13e9 100644
    --- a/mm/mempolicy.c
    +++ b/mm/mempolicy.c
    @@ -1012,6 +1012,9 @@ int do_migrate_pages(struct mm_struct *mm,
    int dest = 0;

    for_each_node_mask(s, tmp) {
    + /* no need to move if its already there */
    + if (node_isset(s, *to_nodes))
    + continue;
    d = node_remap(s, *from_nodes, *to_nodes);
    if (s == d)
    continue;
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      Last update: 2012-03-22 19:17    [W:0.024 / U:88.208 seconds]
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